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If one is added to both the numerator and the denominator of a fraction, the result is [tex]\frac{4}{5}[/tex]. If 5 is subtracted from both the numerator and the denominator, the result is [tex]\frac{1}{2}[/tex]. What is the fraction?

Sagot :

Sure! Let's solve this problem step-by-step.

Let's denote the numerator of the fraction as [tex]\( x \)[/tex] and the denominator as [tex]\( y \)[/tex].

We are given two conditions:
1. If 1 is added to both the numerator and the denominator, the result is [tex]\( \frac{4}{5} \)[/tex].
2. If 5 is subtracted from both the numerator and the denominator, the result is [tex]\( \frac{1}{2} \)[/tex].

Using the first condition, we can write the equation as:
[tex]\[ \frac{x + 1}{y + 1} = \frac{4}{5} \][/tex]
Cross-multiplying to eliminate the fraction, we get:
[tex]\[ 5(x + 1) = 4(y + 1) \][/tex]
Expanding the equation:
[tex]\[ 5x + 5 = 4y + 4 \][/tex]
Rearranging terms to isolate [tex]\( x \)[/tex] and [tex]\( y \)[/tex]:
[tex]\[ 5x - 4y = -1 \quad \text{(Equation 1)} \][/tex]

Now, using the second condition, we can write the equation as:
[tex]\[ \frac{x - 5}{y - 5} = \frac{1}{2} \][/tex]
Cross-multiplying to eliminate the fraction, we get:
[tex]\[ 2(x - 5) = 1(y - 5) \][/tex]
Simplifying the equation:
[tex]\[ 2x - 10 = y - 5 \][/tex]
Rearranging terms to isolate [tex]\( x \)[/tex] and [tex]\( y \)[/tex]:
[tex]\[ 2x - y = 5 \quad \text{(Equation 2)} \][/tex]

Now, we have a system of linear equations:
1. [tex]\( 5x - 4y = -1 \)[/tex]
2. [tex]\( 2x - y = 5 \)[/tex]

We can solve this system using the method of substitution or elimination. Here, we'll use elimination.

First, multiply Equation 2 by 4 to align the coefficients of [tex]\( y \)[/tex]:
[tex]\[ 4(2x - y) = 4 \cdot 5 \][/tex]
[tex]\[ 8x - 4y = 20 \quad \text{(Equation 3)} \][/tex]

Now, subtract Equation 1 from Equation 3:
[tex]\[ (8x - 4y) - (5x - 4y) = 20 - (-1) \][/tex]
Simplifying:
[tex]\[ 3x = 21 \][/tex]
[tex]\[ x = 7 \][/tex]

Now, substitute [tex]\( x = 7 \)[/tex] back into Equation 2:
[tex]\[ 2(7) - y = 5 \][/tex]
[tex]\[ 14 - y = 5 \][/tex]
[tex]\[ y = 9 \][/tex]

So, the numerator [tex]\( x \)[/tex] is 7, and the denominator [tex]\( y \)[/tex] is 9.

Thus, the fraction is:
[tex]\[ \frac{7}{9} \][/tex]